Bifunctional air or oxygen depolarization cells are generally well known in the art. Electro-chemical cells of this type include a gas diffusion electrode capable of generating electricity by electro-chemically combining an oxidizable reactant with a reducible reactant. Generally, these electro-chemical cells are comprised of spaced apart electrodes ionically connected by an electrolyte.
Illustrative of these types of cells and electrodes is the teaching of Buzzelli, U.S. Pat. No. 3,977,901. In that patent, particular types of low surface area carbon black materials were used to help solve problems of electrolyte flooding. Other components used in the electrodes of that patent included 0.5 to 4 parts, per 1 part carbon, of an oxygen evolution material, such as WS.sub.2 or WC, and effective amounts of both a bonding/nonwetting agent and a catalyst for decomposition of perhydroxides, such as silver.
The Buzzelli electrodes were found to have third cycle charging potentials of about 550 mV. to 585 mV., vs. a Hg/HgO reference electrode, achieved by using major amounts of oxygen evolution material, adding substantially to the cost and weight of the electrode. Liu et al., in U.S. Pat. No. 4,341,848, recognized the desirability of lowering this charging voltage, to conserve energy, reducing the amount of silver catalyst that had heretofore dissolved in the electrolyte, and lowering the cost and weight of the above-described types of electrodes.
Liu et al., in the above mentioned patent, substituted ground, elemental sponge iron, formed by thermally reducing Fe.sub.2 O.sub.3 to Fe.degree. in a hydrogen gas atmosphere at about 750.degree. C., for 50% to 100% of the oxygen evolution material of the Buzzelli electrode. Liu et al. also included a metal sulfide as a silver protection additive. However, the elemental sponge iron could oxidize upon storage, and so had a short shelf life, and could corrode during cell operation. The sponge iron formation also required expensive equipment and expenditure of large amounts of energy. Additionally, while the Liu et al. electrodes had low third cycle charging potentials of about 510 mV. to 575 mV. vs. a Hg/HgO reference electrode, their stability and cycle life could be improved. What is needed is an active electrode material having a long shelf life, and which will provide low charging potentials, minimal electrolyte flooding, and up to 500 cycles of steady performance life.